The invention relates to a deflection unit for a cathode ray tube, which deflection unit comprises a line deflection coil, a field deflection coil surrounding the line deflection coil, the field deflection coil comprising wire strands and having first void spaces between the wire strands, and a yoke ring surrounding the field deflection coil, second void spaces being present between the field deflection coil and the yoke ring.
The invention also relates to a cathode ray tube comprising such a deflection unit.
The invention further relates to a method of manufacturing a deflection unit for a cathode ray tube.
A deflection unit comprising a field deflection coil and a line deflection coil, in which the field deflection coil comprises wire strands and has void spaces between the wire strands, is known from WO-A 98/26574. A deflection unit of this type is generally constructed in such a way that the two coils are mounted on a hollow support (one on the inner side and one on the outer side) and that a yoke ring surrounds these coils. The purpose of the yoke ring is to short-circuit the magnetic lines of flux outside the coils, which are generated by the field deflection coils during operation. The yoke ring thus reduces unwanted external magnetic stray fields. This also leads to an increase of the sensitivity of the line deflection. Although the presence of a yoke ring helps to reduce these magnetic stray fields, a further reduction is desired.
It is an object of the invention to provide a deflection unit for a cathode ray tube wherein the sensitivity of the line deflection is improved.
The deflection unit according to the invention is characterized in that the first and/or second void spaces are filled with a magnetic material. The application of a magnetic material in the first and/or second void spaces improves the short-circuiting of the magnetic lines of flux outside the line deflection coils, reduces the unwanted magnetic stray fields and increases the sensitivity of the line deflection.
An embodiment of the invention is characterized in that the magnetic material comprises a plastic deformable magnetic material. The use of a plastic deformable material provides a way of accurately filling the voids and proper adaptation to the local shape of the voids.
A further embodiment of the invention is characterized in that the deformable magnetic material comprises a resinous material, which comprises a filler of magnetic particles. This embodiment has the advantage that the concentration of magnetic particles may be freely chosen and can be optimized to the application.
A further embodiment of the invention is characterized in that the yoke ring is adhered to the field deflection coil by means of the resinous material. This embodiment has the advantage that an additional adhesive necessary for connecting the yoke ring to the field deflection coil is not required; this helps to reduce the cost price of the deflection unit.
A second aspect of the invention provides a cathode ray tube assembly comprising such a deflection unit.
A third aspect of the invention provides a method of manufacturing such a deflection unit as defined in claim 6.
These and other aspects of the invention will be elucidated with reference to the embodiments described hereinafter.